Apparatus for melting ice

ABSTRACT

A surface effect drilling vehicle with ice melt apparatus has a hollow hull lined with a fibrous material and a low vapor pressure liquid therein. Heat is applied to the hull&#39;&#39;s interior wall which vaporizes the liquid causing the liquid to transfer by diffusion to the exterior wall of the hull where it loses its heat to the ice and condenses. By the capillary action of the fibrous material the condensed liquid returns to the heated hull interior wall where the process is repeated.

United States Patent 11 1 1111 3,837,131 1 Lea, Jr. 1 Sept. 24, 1974 [5 APPARATUS FOR MELTING ICE 3,665,886 4/1972 German 114/40 3,677,329 7/1972 Kirkpatrick 165/105 [75] Inventor- James Rlchardso! 3,681,927 8/1972 Duc, Bonnamy 61/72.1 [73] Assigneez Sun on Company, Dallas, 3,749,162 7/1973 Anders 114/.5 D 22 Filed: Oct. 5, 1972 OTHER PUBLICATIONS Kurt Lawrence, A Conceptual Study of the Artic [21] APPl- 295,312 Drift Barge, 12-16-66, 1-1 to ,1-12.

[52] US. Cl 114/.5 D, 114/40, 165/105, Primary ExaminerRobert .1. Spar 166/.5 Assistant Examiner-G. L. Auton [51] Int. Cl B63b 35/00, B63b 35/08 Attorney, Agent, or FirmGe0rge L. Church; Donald [58] Field of Search 114/.5 D, .5 F, 40, 41; R. Johnson; John E. Holder 306 A; 180/116, 117; 175/7, 5; 244/15 C, [57] ABSTRACT 134; 166/5 A surface effect drilling vehicle with ice melt apparatus has a hollow hull lined with a fibrous material and [56] References C'ted a low vapor pressure liquid therein. Heat is applied to UNITED STATES PATENTS the hull s interior wall which vaporizes the liquid caus- 2,541,328 2/1951 Bokler 1.; 126/360 R ing the liquid to transfer by diffusion to the exterior 2,774,856 12/1956 Paulsen.... 126/360 R wall of the hull where it loses its heat to the ice and 2.7 1 /19 4 Wya t 165/105 condenses. By the capillary action of the fibrous mateg 2 rial the condensed liquid returns to the heated hull inyr 3,640,517 2/1972 Sendt 165/105 tenor wall where the process repeated 3,664,437 4/1972 McCulloch 166/.5 11 Claims, 2 Drawing Figures .PAIENKDSEPMQM v I @837. 311

APPARATUS FOR MELTING ICE BACKGROUND OF THE INVENTION At the present time there is increasing exploration and drilling activity in the Canadian Arctic region. There have been a number of wells drilled onshore and the logistics related to these wells have been hampered by the environment sometimes requiring air transportation of both drill rig and supplies. This is in part necessitated by ice and snow making overland travel extremely difficult or impossible as a practical matter.

When, however, offshore wells are contemplated the ice problem affects the drilling operation in addition to the problem of logistics. The drilling problem is caused by ice covering most offshore waters during the long winter season. In some areas there is an ice covering year round. The movement of such ice, if fairly thick, exerts tremendous forces on any stationary structure. A conventional offshore drilling platform therefore is not usable in most Arctic offshore regions except in the short summer season in the open areas. Even in the summer some open areas are subjected to free floating sections of ice which could destroy a conventional platform. It thus appears that expensive drilling systems underneath the ice must be utilized or the ice must be dealt with.

If an offshore platform or vessel are utilizedthey must be able to maintain a substantially fixed position relative to the borehole. If ice is moving toward one of these drilling systems it is necessary to clear a path through the ice to keep the drilling apparatus in position. In some areas where floating ice is encountered the ice is removed in several different ways. A high strength platform can be used to shear a path through the ice, however, this procedure cannot be used where thick ice is encountered because of the tremendous forces exerted by thick ice. Explosives can be used to fragment the floating mass of ice into smaller pieces to allow the pieces to deflect past the drilling platform or vessel. lf thick ice is fragmented by explosives the ice chunks could be large enough to cause damage and the large amount of explosives would be expensive. Methods of ice removal used in rivers to prevent build up at bridges includes rotating grates for breaking up the ice and similar apparatus. All of these systems are impractical in Arctic offshore areas where the ice is fairly thick. Ice 6-10 feet thick is common in certain of the arctic offshore regions.

One method of coping with the ice movement is to melt a path through it with hot plates thus eliminating the ice debris problem. Obvious problems in such a melt system are l) inefficient heat distribution and 2) the development of hot spots causing failure in the structure of the melt system.

Hot spots have two primary causes: I the placement of the heat source on the melting plate, and 2) the absence of contact between portions of the melting plate and the ice mass.

The first cause results from the necessity of having discrete heat sources, rather than a heat source uniform over the entire surface area of the melting element. A uniform heat source is not practical due primarily to the cost and weight of the plumbing required. The areas of the melting element in front of the discrete heat sources receive the larger portion of the heat supplied. Those areas of the melting element between the LII heating elements are much further from the heat sources and consequently much of the originally supplied heat is either lost or consumed before reaching them. Thus, temperatures in the vicinity of the heat sources are excessive creating hot spots, while the other portions are left at a much lower temperature.

The second cause results from irregularities in ice formations. In one case, the surface of the ice mass may drop below the top of the melting element and in another the melting element may encounter air cavities in the ice. In both situations the heating element comes into contact with air rather than ice. Since air conducts heat much less readily than ice, those areas of the melting element in contact with the air will retain heat and become overheated.

Heat spots are detrimental in several ways. First, they necessitate the use of highly heat resistant metals for the construction of the melting elements. The elements must be designed to withstand the hot spot temperatures rather than an average temperature of the entire element. Lighter and less expensive metals such as aluminum could not be used since even relatively low temperatures will cause changes in their crystalline structures reducing strength and causing brittleness. For example, pure aluminum, although it melts at 1220.4F, loses three-fourths of its tensile strength between F and 400F, the temperature range in which ice melting apparatus would typically operate. Thus, if hot spots could be eliminated, melting elements could be practically designed using aluminum or similar metals to operate at an average temperature within the strength tolerance range of the metal rather than having to allow for an isolated maximum hot spot temperature.

Second, hot spots slow the maximum rate at which ice may be melted. As noted above, the maximum hot spot temperature must be taken into account to prevent material failure. This limits the total amount of heat that can be delivered to the melting element, since increased heat supply results in a higher hot spot temperature, which may exceed the material failure critcal temperature. If the hot spots could be eliminated, a larger amount of heat could be supplied to the melting element without the risk of exceeding the critical temperature. The melting rate of the ice depends upon the amount of heat supplied and an increase would thus result in more rapid melting.

It is therefore an object of the present invention to provide an apparatus for melting ice whose melting element exhibits improved heat conduction and distribution characteristics.

SUMMARY OF THE INVENTION In accordance with one embodiment of the invention, a melting element having a hollow cavity is used. The cavity is lined with a fibrous metallic material leaving a central void. The fibrous material is wetted with a fluid having a low vapor pressure.

When heat is applied to the rearward side of the melting element, the fluid in the rearward position of the fibrous lining evaporates. The vapor traverses the central void by diffusion and distributes the heat uniformly across the forward portion of the melting element.

When the vapor reaches the forward portion, it loses its heat to the ice and subsequently condenses. The condensate is then carried by capillary action back to the rearward portion of the fibrous lining to begin the cycle anew.

In accordance with another embodiment, the lateral portions of the hull of an ice melting vehicle is hollowed and lined with the wetted metallic fibrous material. The interior of the hull is heated, and the vaporized liquid diffuses to uniformly distribute the heat to the hull exterior to melt the ice.

DESCRIPTION OF THE DRAWINGS FIG. 1 shows an Arctic drilling vehicle using the invention to melt a path through a moving air mass.

FIG. 2 is a cross-section of the lateral portion of the Arctic vehicles hull.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. I there is shown an Arctic vehicle which could utilize the invention in one of its embodiments. An air cushion vehicle 10, usually called a hovercraft, is adapted to serve as a floating drilling platform. It is shown floating in a cavity 14 in an ice mass 12 which covers a body of water 16.

The hovercraft 10 is equipped with a drilling derrick 18 located on the deck of the hovercraft. A drill stem 20 extends from the derrick 18 through the hovercraft superstructure 22 and hull 24 into the body of water 16 to the ocean floor 26., where a hole 28 is being drilled by drill bit 30. The forward edge 32 of hull 24 is shown melting a portion 34 of ice mass 12.

The hovercraft It) can be self-propelled allowing it to travel independently to the desired drillsite. During terrestrial operation, the hull 24 has a skirt (not shown) extending downwardly therefrom for operating the hovercraft in a hover mode. The skirt creates a cavity, or plenum, which acts to support the hovercraft 10 when the plenum is filled with air. The air is provided by compressors located within the hovercraft and is transmitted to the plenum by means of several passageways extending through the bottom of hull 24. The compressors fill the plenum with air. and when a sufficient pressure is reached, the hovercraft will be lifted off the ground on a cushion of air.

The air cushion allows the hovercraft to traverse irregular terrain not possible with normal wheeled vehicles to reach remote drilling sites, such as the ice covered portions of the Arctic Ocean. Once at a desired drilling site, a cavity 14 (FIG. 1) large enough to accomodate the hovercraft is blasted in the ice mass 12 using suitable explosives, if a cavity has not already been created by failure of the ice caused by the weight or effect of the hovercraft. Once the hovercraft is located in the cavity 14 the hull 24 allows the hovercraft to float like an ordinary boat. Once afloat the previously mentioned skirts are retracted and the drilling equipment is deployed.

After drilling has begun, it is necessary to maintain the hovercraft in a fixed position relative to the ocean floor. Otherwise the drill stem 20 will be bent or broken making further drilling impossible. The movement 36 of the Arctic ice mass I2 is the main concern of using a hovercraft for drilling in the offshore Arctic. To compensate for such ice movement, the hull 24 of the hovercraft I is heated in order to melt the encroaching ice. The effect is to enlarge cavity 14 in the direction opposite the ice movement. This allows ice mass 12 to move past the hovercraft without changing the hovercraft location.

The entire periphery of the hull 17 can be heated to allow for ice movement in any direction. In FIG. 1 the ice movement 36 is depicted as occurring from right to left. This brings the melting surface 32 of hull 24 into contact with face 38 of ice mass 12. Heat 40 transfers from the hull face 32 causing the ice face 38 to recede to the right due to melting as the ice mass 12 moves to the left. As can be envisioned by examination of FIG. 1, if the ice is quite thick, a portion of the ice could pass under the hovercraft and impinge the drill string. Therefore, a moon pool may be needed to protect the drill string by melting a narrow band of ice through which the drill string can pass. It is likely that the weight of the hovercraft will crush any ice passing beneath it or the ice may melt when submersed.

FIG. 2 shows a cross section of a portion of the hovercrafts hull shown in FIG. 1. The hull 24 has a hollow cavity 42 enclosed by shell 44. Shell 44 has an interior shell portion 46; an exterior shell portion 48; and interior face 50; and a melting surface 32. The interior sur face of shell 44 is lined with a wick 52 made of a fibrous metallic material. The wick can also be formed of any other non-absorbent heat resistant material such as a flberized silica material. Wick 52 has an inner portion 54 and an outer portion 56. Inside the wick 52 there is a vapor cavity 58. The wick 52 is permeated with a fluid having a relatively low vapor pressure. As depicted, heat is supplied to the hull interior face 50 by pipes 60 through which a hot liquid is circulated, although many other types of heat sources may be used such as gas flame or exhaust gas from engines used for drilling.

In operation, heat 62 is conducted from pipes 60 through the interior shell portion 46 into the wick inner portion 54. The liquid in wick inner portion 54 absorbs the heat and evaporates into the vapor cavity 58. The heat laden vapor 64 randomly migrates to all parts of wick outer portion 56 by diffusion. The vapor 42 releases its heat in wick outer portion 56 and condenses into liquid form. Heat 66 is conducted through hull shell exterior portion 48 to the ice mass 12. The ice mass 12 absorbs the heat and then melts. The condensed liquid in wick outer portion 56 is then transferred by capillary action through the wick 52 back to wick inner portion 54 as indicated by arrows 68. There the entire process is begun again.

This hull design is effective in solving the problem of hot spots which plague current ice melting systems.

The hot spots resulting from the necessity of discrete heat sources are eliminated by this vaporization process within the hulls hollow portion 42. Heat 62 emanating from heat pipes 60, or another heat source, evaporates the liquid in rear wick portion 54. The resulting vapor rapidly expands to fill cavity 58. This expansion evenly distributes the heat laden vapor molecules uniformly throughout the cavity by the process of diffusion. The uniformly distributed vapor molecules act as a uniform heat source at wick outer portion 56 where they give up their heat to the ice mass 12 and return to the liquid state.

The other variety of hot spots, resulting from absence of contact between the ice and the melting surface is alleviated by a similar process. When a portion of hull face 32 loses contact with the ice, the heat is not removed from the hull portion 48 rapidly enough to prevent local overheating. In that case, the liquid in the wick outer portion 56 adjacent the hot spots will vaporize and enter cavity 58. The vaporization process requires heat, and that heat is extracted from the hot spot. The heat is then distributed to the other portions of the melting surface 32 by the aforementioned processes of vapor diffusion and condensation.

It is difficult to make generalities about the amount of heat needed to melt the ice due to variations in the speed of ice movement and ice thickness. Contact pressure of the heating surface on the ice sheet as well as the amount of heated surface area applied to the ice, effect the speed of melting. The heated area being applied to the ice can be increased by slanting the heating source from vertical.

Even though the rate of ice melting is contingent on a number of variables it has been determined that the heating face temperature can be below some 100F if less than 100 feet of ice/day is being melted and 20 pounds per square foot of contact pressure is maintained between the heating face and the ice. It thus would appear that a suitable liquid for use in the cavity 42 of hull 24 would be water under a vacuum such that the vaporization temperature of the water is around 140-l 80F. This vaporization temperature allows both an efficient melting rate as well as the use of less expensive materials in the hull adjacent the heating surface. In addition, other fluids which vaporize at temperatures below some 200F can be utilized. In order for the fluid to operate effectively for ice melting the condensation temperature of the fluid should be somewhat in excess of the melting temperature of the ice.

It is believed that the operation of the above described apparatus will be apparent from the foregoing description. While particular apparatus has been shown and described as suitable for melting ice relative to an Arctic vehicles hull, it is obvious the concept can be used with other crafts and structures. In addition, various changes and modifications may be made to the present invention without departing from the spirit and scope of the invention, as defined in the annexed claims.

What is claimed is:

1. In an Arctic vessel, means for melting ice, which comprises: a heat source; and a melting member for transferring heat from the heat source to the ice comprising: a lateral hull portion of said vehicle having an enclosed cavity; a fibrous capillary lining the interior of the cavity arranged to leave a central void; and a liquid, having a low vapor pressure, permeating the fibrous material.

2. The vehicle of claim 1 wherein the hull indicates a multiplicity of cavities lined with a capillary and having water located in the cavity.

3. The vehicle of claim 2 wherein 'the water is under a partial vacuum to lower the vaporization temperature of the water.

4. The vehicle of claim 1 where the liquid has a vaporization temperature below 200F and a condensation temperature above the melting temperature of the ice.

5. The vehicle of claim 1 wherein the fibrous capillary is a non-absorbent heat resistant material.

6. In an air cushion vehicle for use in Arctic regions, means for melting ice which comprises: a heat source; a melting member for transferring heat from the heat source to the ice comprising: a solid bottom portion; a lateral portion having an enclosed cavity; a fibrous wick lining the interior of the cavity arranged to leave a central void; and a liquid, having a lower vapor pressure, partially filling the cavity.

7. The vehicle of claim 6 wherein the fibrous wick is arranged to form a hollow volume enclosed by the wick which volume acts as a vapor diffusing zone.

8. The vehicle of claim 6 wherein the liquid is water in sufficient amount to saturate the wick.

9. In a floatable hovercraft vehicle for drilling in Arctic regions, a means for melting ice, which comprises: a plurality of heat sources; an inner hull portion adjacent the heat sources, for conducting heat away from the heat sources; an inner fibrous wick adjacent the inner hull portion; a liquid having a low vapor pressure, filling the inner wick means, which liquid absorbs heat from the inner hull means and thereby vaporizes; a vapor chamber, adjacent the inner wick means, into which vapor produced in the inner wick means escapes; an outer fibrous wick adjacent the vapor chamber connected at its extremities to the inner wick, into which vapor from the vapor chamber releases its heat and condenses into a liquid, said liquid returning through'the outer wick portion to the inner wick portion; and an outer hull portion, for conducting heat from the outer wick portion to the ice.

It). In a floatable hovercraft vehicle, having a hull and used for drilling in Arctic regions, a means for melting ice, which comprises: a plurality of heat sources; an inner hull portion adjacent the heat sources; an inner capillary material for transferring liquids, lining the inner hull portion; an outer hull portion adjacent the hovercraft environment; an outer capillary material lining the outer hull portion; a vapor chamber located between the inner and outer capillary materials; a central capillary material connecting the peripheries of the inner and outer capillary materials; a connecting hull portion joining the inner and outer hull peripheries in a manner to provide an enclosed chamber lined with capillary material; and a fluid located in the enclosed chamber having a vaporization temperature below 250F.

11. The vehicle of claim 10 wherein the outer hull portion is angled from vertical and wherein the condensation temperature of the fluid is above the melting temperature of the ice. 

1. In an Arctic vessel, means for melting ice, which comprises: a heat source; and a melting member for transferring heat from the heat source to the ice comprising: a lateral hull portion of said vehicle having an enclosed cavity; a fibrous capillary lining the interior of the cavity arranged to leave a central void; and a liquid, having a low vapor pressure, permeating the fibrous material.
 2. The vehicle of claim 1 wherein the hull indicates a multiplicity of cavities lined with a capillary and having water located in the cavity.
 3. The vehicle of claim 2 wherein the water is under a partial vacuum to lower the vaporization temperature of the water.
 4. The vehicle of claim 1 where the liquid has a vaporization temperature below 200*F and a condensation temperature above the melting temperature of the ice.
 5. The vehicle of claim 1 wherein the fibrous capillary is a non-absorbent heat resistant material.
 6. In an air cushion vehicle for use in Arctic regions, means for melting ice which comprises: a heat source; a melting member for transferring heat from the heat source to the ice comprising: a solid bottom portion; a lateral portion having an enclosed cavity; a fibrous wick lining the interior of the cavity arranged to leave a central void; and a liquid, having a lower vapor pressure, partially filling the cavity.
 7. The vehicle of claim 6 wherein the fibrous wick is arranged to form a hollow volume enclosed by the wick which volume acts as a vapor diffusing zone.
 8. The vehicle of claim 6 wherein the liquid is water in sufficient amount to saturate the wick.
 9. In a floatable hovercraft vehicle for drilling in Arctic regions, a means for melting ice, which comprises: a plurality of heat sources; an inner hull portion adjacent the heat sources, for conducting heat away from the heat sources; an inner fibrous wick adjacent the inner hull portion; a liquid having a low vapor pressure, filling the inner wick means, which liquid absorbs heat from the inner hull means and thereby vaporizes; a vapor chamber, adjacent the inner wick means, into which vapor produced in the inner wick means escapes; an outer fibrous wick adjacent the vapor chamber connected at its extremities to the inner wick, into which vapor from the vapor chamber releases its heat and condenses into a liquid, said liquid returning through the outer wick portion to the inner wick portion; and an outer hull portion, for conducting heat from the outer wick portion to the ice.
 10. In a floatable hovercraft vehicle, having a hull and used for drilling in Arctic regions, a means for melting ice, which compRises: a plurality of heat sources; an inner hull portion adjacent the heat sources; an inner capillary material for transferring liquids, lining the inner hull portion; an outer hull portion adjacent the hovercraft environment; an outer capillary material lining the outer hull portion; a vapor chamber located between the inner and outer capillary materials; a central capillary material connecting the peripheries of the inner and outer capillary materials; a connecting hull portion joining the inner and outer hull peripheries in a manner to provide an enclosed chamber lined with capillary material; and a fluid located in the enclosed chamber having a vaporization temperature below 250*F.
 11. The vehicle of claim 10 wherein the outer hull portion is angled from vertical and wherein the condensation temperature of the fluid is above the melting temperature of the ice. 